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LED Quality

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Deozaan:
It just gives me the urge to defecate......
-Tinman57 (January 03, 2013, 08:25 PM)
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Us 'Mericans have got just the "supplement" to help with that problem!

Tinman57:
It just gives me the urge to defecate......
-Tinman57 (January 03, 2013, 08:25 PM)
--- End quote ---

Us 'Mericans have got just the "supplement" to help with that problem!
-Deozaan (January 04, 2013, 06:07 AM)
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  Considering that I'm a natural born 'Merican, I'm pretty well versed in the "supplements" here.

SeraphimLabs:
Depends more on the fixture than the LED itself.

I've had amazingly good results with LED floodlights from RAB. They are being used as dusk to dawn security lighting, each 39W fixture being a rated equivalent to a roughly 150W Metal Halide floodlight in similar applications.

Haven't yet gotten to try other RAB fixtures besides their floodlights and wallpacks operating as dusk to dawn security lights, but they seem to be one of the brands that actually has this down.

Something I did notice though is many replacements for Halogen floodlights in fact use slightly more power than the compact flourescent versions, although the tradeoff is the CFL versions take a few minutes to reach full intensity in cold weather while the LED lamps are instantly at full power.

Definately though, don't trust the knockoffs. Because LEDs generally produce light from a cluster of emitting surfaces instead of a single wire or tube they are very sensitive to the design of the reflector and the fixture they are used in.

For the most part though applications that do not need cold weather performance will be fine with compact flourescent type lights until the LED market stabilizes and the poor quality brands get a deserving reputation to identify what brands are to avoid.

I do have some LED powered Par38 lamps serving inside machines though. Although their efficiency is only barely better than a CF type equivalent, they do have the added advantage of being vibration resistant- something needed in a machine that is prone to shaking half the building.


Also fine print. LEDs do produce some heat, although not much by themselves. It is their power supplies that need the heatsinks and are responsible for most of the efficiency loss. But overall the heat output of a well built LED will be significantly lower than any other type of light.

Tinman57:
Something I did notice though is many replacements for Halogen floodlights in fact use slightly more power than the compact flourescent versions, although the tradeoff is the CFL versions take a few minutes to reach full intensity in cold weather while the LED lamps are instantly at full power.
-SeraphimLabs (January 04, 2013, 03:47 PM)
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  I have track lighting in one of my bathrooms.  I put 5 of the the 11W compact fluorescent bulbs in it to replace the 8 25W Bombilla's.  They are truly brighter than all of the 25 watt bulbs, but it takes them about two minutes to get to a reasonable brightness, and about 5 minutes to full brightness.  That's the only sucky thing about them, they save energy but if you have anything that you need to do that requires good lighting you have to turn them on a few minutes in advance.  I guess the good thing about that is when you get up in the middle of the night to use the restroom you don't have blinding lights to contend with.  lol

4wd:
I wasn't going to reply but then I thought "screw it" :)

Just to be sure we're talking about the same thing, this is about White High Performance LEDs which are generally what are used in incandescent replacements.

Also fine print. LEDs do produce some heat, although not much by themselves. It is their power supplies that need the heatsinks and are responsible for most of the efficiency loss.-SeraphimLabs (January 04, 2013, 03:47 PM)
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Every LED replacement I've seen, used and built is the exact opposite - the LED generates most of the heat.  They don't produce radiant infrared heat, (as incandescent bulbs do), but the semi-conductor junction within them produces a lot of heat that needs to be dissipated via conduction.

Maximum junction thermal temperature for LEDs is normally specified at ~150°C by manufacturers, (CREE, Luxeon, etc), in their datasheets - at that temperature the LED lifespan is greatly reduced, (eg. from ~100,000 hours @ 30°C to ~10,000 @ 150°C), and luminous output is also reduced.

LEDs are usually supplied thermally bonded to an aluminium slug, this then should be mounted on a heatsink sufficient to reduce the LEDs junction thermal temperature for extended life.

The RAB floodlight you mention uses three 13W LED chips, each of which consist of ~9 LED emitters arranged in 3 columns.

Here's a LED Junction Temperature calculation for a 6 emitter 11.76W chip:
Calculating LED Junction Temperature in Lighting Applications

A calculated junction temperature of 262.9°C.

Here's a calculation for the heatsink requirements of a 14.6W LED chip:
How to calculate your LED heat sink

Drivers for LEDs are very efficient these days, anywhere from 80-95% - you can get them for outputs up to 20W or more that don't need heatsinks - even the 70W versions are in small metal boxes that don't require any extra heatsinking.

The RAB 39W floodlights use the whole front of the floodlight, (reflector/housing), as one big heatsink with fins to ensure the LEDs stay cool enough to achieve their 100,000 hour rating.

If you were to open it up, remove the LEDs from the housing and just hold them while you turned it on, I pretty much guarantee you won't be holding them for long.

The exact same thing can be seen in the MR-16 (12V AC/DC) and GU-10 (90-265V AC) replacements, the LEDs are mounted on the heatsink, the drivers have none.

The author of the junction temperature calculation above mentions that ~70% of the input power to the LED is converted to heat.

Fact or Fiction – LEDs don’t produce heat

And FWIW, here's an article on how to drive an LED at over 100% efficiency but at 69 picowatts of of optical output I don't think you'll be lighting up the backyard any time soon. :)

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